This invention relates to fluid circulating systems as they include an accumulator-reservoir device of the bootstrap type. More particularly, the invention is concerned with devices as identified incorporating a flexible, rolling diaphragm which changes convolution in response to movements of a reciprocable fluid pressure operated piston.
In prior art systems, the accumulator-reservoir device accommodates fluid expansion due to temperature increases by a yielding motion of the piston in one sense. Decreasing temperatures, which bring about a greater fluid density, are compensated for by a pressured movement of the piston in the opposite sense, this being a function of operation of the pump which has a connection at its outlet side to the accumulator-reservoir device. While the pump operates, the fluid pressure it applies is effective yieldingly to bias the piston in the accumulator-reservoir device and is applied also in a manner to maintain the rolling diaphragm in a convolution appropriate to the position assumed by the piston. A normal operating condition of the system finds the piston displaced a distance against the effects of pump pressure since the fluid is at this time warm and relatively expanded. If the pump now is shut off, the system cools and fluid density is reduced. The pressure of ambient surroundings is available to move the piston in the accumulator-reservoir device to obviate a creation of sub-ambient fluid pressures in the device. In some instances, however, friction effects sufficiently retard piston movement that the rolling diaphragm, also subject to the pressure of ambient surroundings, moves relatively to the piston and assumes an inverted attitude between the piston and an enclosing housing out of a proper convolution. Now, when the pump is again turned on, a pressured movement of the diaphragm to its correct position is attempted with what is sometimes damaging effect upon the diaphragm.
Temperature changes, referred to in the foregoing, occur as a result of changing ambient temperatures and as a result of placing the system in operation and of discontinuing such operation.